To begin, there is the shooter himself, Omar Mateen, who had two acting credits according to the Internet Movie Database (IMDb). A day after I took the screenshot below, IMDb saw fit to delete one of them — Mateen's appearance in the documentary, The Big Fix. 

Then there is eyewitness Luis Burbano who claims to be in Pulse at the time of the shooting and admitted that he was the man who had held an exit door closed, ostensibly to keep the armed gunman from escaping, which makes no sense. What Burbano actually achieved was to prevent survivors from leaving the club.

On IMDb, Burbano is identified to have five acting credits. A day after I had taken a screenshot of his acting credits (see below), IMDb also scrubbed one of the credits — Burbano's portrayal of a "club patron" in the 2015 music video "Spirit of Orlando: Shooting Up".